1. Field of the Invention
The present invention relates to an expression converting method, an expression converting apparatus and a program that convert the expression of an input sentence and output an expression into which the expression of the input sentence is converted, for example, to an expression converting method, an expression converting apparatus and a program that perform language conversion such as translation or interpretation, sentence pattern conversion to convert written language into spoken language, or summary creation to summarize a complicated or redundant sentence and output a summary.
2. Description of the Related Art
A conventional technology will be described with an interpretation software program as an example.
An interpretation software program comprises voice recognizing means and language translating means, and realizes interpretation by successively executing voice recognition for converting a voiced sentence input as an acoustic signal into an output sentence represented as a word text string, and language translation as expression conversion to translate an input sentence represented as a word text string into a sentence in another language.
The language translating means executing language translation in a manner as described above comprises: language analyzing means of analyzing the syntactic or semantic construction of the input sentence; language converting means of converting the input sentence into another language based on the result of the analysis; and output sentence generating means of generating a natural output sentence from the result of the translation.
In interpretation software programs and some translation software programs, to correctly translate ungrammatical casual expressions which are frequently used in spoken language, a technique is frequently used such that a language analysis according to grammatical rules is not performed but sentence examples similar to actually input sentences are learned and the similar sentence examples are searched to perform language analysis. An example of such conventional interpretation software programs will be described with reference to the example shown in FIG. 8.
Here, a case will be described in which a voiced sentence example in Japanese is interpreted into a voiced sentence example in English. The language to be interpreted will be referred to as the original language, and the language into which the original language is to be interpreted will be referred to as the target like to reserve a room,” and these are divided into the following two bilingual phrases: (A) “heya no yoyaku ()” and “reserve a room” as the bilingual phrase (A) 71; and (B) “onegai shitain desuga ()” and “I'd like to” as the bilingual phrase (B) 72.
The content words such as “heya (),” “yoyaku ()” and “onegai ()” are represented as variables X, Y and Z, respectively, by use of a classified vocabulary table 64 previously created as shown in FIG. 9-2(e). Here, the classified vocabulary table 64 is a table listing the content words which the variables can take as their values. For example, the variable X takes a value such as “heya (),” “kaigishitsu ()” or “kuruma (),” and the content word “heya ()” is a value which the variable X can take. Therefore, the content word “heya ()” of the bilingual phrase (A) 71 is replaced with the variable X.
In this manner, two bilingual phrase rules (A) “X no Y (X  Y)” “YX” and (B) “Z shitain desuga ()” “I'd like to” are written into the bilingual phrase dictionary 62.
In order that the ordinal relations of the phrases are made rules, as shown in FIG. 9-2(d) as an inter-phrase rule 63, inter-phrase relations such as “(A) o (B) ((A)  (B))” “(B) (A)” are stored in the inter-phrase rule table 63. This processing is performed on all the voiced sentences in the bilingual corpus 1.
In performing interpretation, first, an original language voice is input to voice recognizing means 64. The voice recognizing means 64 outputs as a voice recognition candidate the acoustically most similar word string, for example, from among the word strings written in the bilingual phrase dictionary 62 as phrases and the word strings that can be presumed from the phrase strings written in the inter-phrase rule 63.
Language translating means 65 receives consecutive word strings recognized in this manner, converts the input consecutive word strings into phrase strings written in the bilingual phrase dictionary 62, and searches for the inter-phrase rule 63 corresponding to each phrase string. Then, the language translating means 65 converts the input original language recognition result sentence into a target language sentence based on the target language phrase equivalent to each phrase and the inter-phrase rule of the target language.
The obtained target language sentence is input to output sentence generating means 66 which corrects grammatical unnaturalness of the target language sentence. For example, the output sentence generating means 66 performs processing such as optimization of a pronoun, a verb and an auxiliary verb, for example, conversion into the third person form, the plural form or the past form, and optimization of the overall structure of the sentence. The target language translation result sentence having undergone the correction is output, for example, as a text.
However, the conventional interpretation software program has, although having an advantage that ungrammatical input sentences can be handled, a problem that since a multiplicity of different bilingual phrases and combinations thereof are written as rules as they are, the conversion rules are complicated and enormous in volume and consequently, it takes much time for the program to perform processing.
Moreover, complicated rules are necessary for the grammar check performed by the output sentence generating portion; particularly, with respect to interpolation of zero pronouns, there is no technology by which zero pronouns can completely and correctly be interpolated, and interpolation is sometimes erroneously performed.
In addition, when a partially erroneous sentence is input to the language translating portion because of a voice recognition error or the like, since language conversion is performed based on erroneous in-phrase and inter-phrase rules, a translation result conveying no intention at all is output.